1. Field of the Invention
The present invention relates to a process for the extraction of uranium from its ores using sulfuric acid. The invention is particularly directed to an extraction at a pH range of 2.5 to 5.5 using sulfuric acid, hydrogen peroxide and a sulfate.
2. Prior Art
It is well known how to recover uranium from its ores by converting the relatively insoluble tetravalent state of uranium in the ore to the soluble hexavalent state. Most of this uranium ore processing employs leaching in dilute sulfuric acid. Normally, this sulfuric acid leaching is carried out at pH.ltoreq.1 with an oxidant added to raise the uranium (IV) to uranium (VI), R. C. Merritt, The Extractive Metallurgy of Uranium, Chapters 5 & 15, (1971), Colorado School of Mines Research Institute. At these pH levels, however, a powerful oxidation phenomenon, known as Fenton's Reagent does not function, as this phenomenon requires hydrogen peroxide, traces of dissolved ferrous ion and an absence of dissolved ferric ion. pH levels of 3 or more preclude dissolved ferric ion and allow the phenomenon to occur, W. G. Barb, J. H. Baxendale, P. George & K. R. Hargrave, "Reactions of Ferrous and Ferric Ions with Hydrogen Peroxide," (received July 1950) Transactions of the Faraday Society. Additionally sufficient iron for the required ferrous ion is present in most uranium ores.
At pH of 2.5 to 6.5 uranium normally forms an insoluble peroxide with hydrogen peroxide, and any extracted uranium under Fenton's Reagent conditions would be reprecipitated and lost, A. R. Amell and D. Langmuir, "Factors Influencing the Solution Rate of Uranium Dioxide under Conditions Applicable to In Situ Leaching" (NTIS-PB299947/AS) Nov. 20, 1978) U.S. Department of Interior Bureau of Mines Contract No. HO272019 Final Report. Sulfates, however, are known to inhibit peroxide precipitation, M. Shabbir & K. E. Tame, "Hydrogen Peroxide Precipitation of Uranium" (MTIS PB-234 691), (July 1974) U.S. Department of Interior Bureau of Mines, and R. A. Brown, "Uranium Precipitation with Hydrogen Peroxide," (February 1980) Society of Mining Engineers of AIME, Littleton, Colo., Preprint No. 80-63.
In in situ leaching of uranium from, for example, porous sandstone deposits, use of low pH leach solutions has continued to cause problems of high levels of acid consumption and impurity pick-up via sulfuric acid attack on gangue material. As a result, this process (acid in situ leaching) has achieved very limited commercialization.
The novel uranium extraction process described hereinafter is applicable to both tank leaching of conventionally mined ores and in situ leaching and results in substantially lower acid requirements.